The present invention generally relates to plotters, scanners and similar devices that use a rotatable drum for mounting films, printing plates or documents that are to be exposed or scanned, and particularly such devices which use vacuum drums.
A number of prior art vacuum drums for handling different sized media involve vacuum drums provided with groove or hole arrangements along with valves or separate vacuum chambers for providing different sized areas of vacuum force over the surface of the vacuum drum. For example, U.S. Pat. No. 5,383,001 (Bosy) discloses a valving system and separate vacuum channels for handling media of different sizes. By adjusting the valves, the vacuum channels may be set to accommodate any of a number of media sizes. It is important that a vacuum be applied about the edges of media being mounted on a vacuum drum. Thus the multi-chambered vacuum drum invented by Bosy may only be used on media having any of the several particular sizes that the drum accommodates. Only several specific sizes are accommodated.
Likewise, U.S. Pat. No. 5,183,252 (Wolber et al.) discloses a vacuum drum with first and second evacuation zones. Each zone includes a number of vacuum holes. An embodiment is shown for accommodating two standard media sizes in which either one or both of the evacuation zones are activated.
Previous vacuum drums having only a single chamber with holes connecting the inner chamber to the surface of the drum used masks to mount smaller films on the drum. A mask was typically L-shaped to block off vacuum holes located beyond the edge of the media to be mounted on the drum. Typically, the mask was an inextensible plastic sheet adhesively attached to the vacuum drum. The sheet would block off the vacuum holes that were located beyond the edges of the media to be mounted, while the media was allowed to be mounted directly to the vacuum drum in the unmasked area.